This invention relates generally to carburetors for internal combustion engines, and more particularly to a flow-regulating carburetor having a movable valve element which is automatically shifted as a function of the mass-volume of the fluids passing through the structure.
A carburetor in accordance with the invention is especially applicable to internal combustion motorcycle and other small automobile engines to so proportion the ratio of combustion air to fuel as to maintain an optimum ratio thereof under varying conditions of load and speed throughout a wide operating range, thereby attaining higher combustion efficiency, significantly increased fuel economy and reduced emission of pollutants.
The function of a carburetor is to produce the fuel-air mixture needed for the operation of an internal combustion engine. In the carburetor, fuel is introduced in the form of tiny droplets in a stream of air, the droplets being vaporized as a result of heat absorption in a reduced pressure zone on the way to the combustion chamber whereby the mixture is rendered inflammable. In a conventional carburetor, air flows into the carburetor through a Venturi tube and a fuel nozzle within a booster Venturi concentric with the main Venturi tube. The reduction in pressure at the Venturi throat causes fuel to flow from a float chamber in which the fuel is stored through a fuel jet into the air stream. The fuel is atomized because of the difference between air and fuel velocities.
In conventional carburetors, the dispersion and vaporization effects resulting from the reduction in throat pressure prevail only during a small part of the operating range of the engine due to the fixed dimensions of the venturi which are usually chosen for midrange performances; hence one must provide idle and slow speed jets from passages and parts at or about the throttle plate to maintain fuel flow at low air flow conditions when Venturi vacuum is insufficient to draw fuel into the Venturi nozzle.
In most modern motorcycles, including the Honda, the Suzuki and Yamaha models manufactured in Japan as well as those made by British, Italian, German and by other manufacturers, use is made of "slide valve" carburetors. While these differ in detail according to the make of the machine, they are all quite similar in outward appearance and in operation. Slide-valve carburetors fall into three distinct classes: the direct-control or DC type, the CV (constant velocity or vacuum) type, and the throttle-plate type.
In the DC-type, the slide valve is laterally inserted into the air flow passage of the carburetor and moves more or less therein to vary the volume of air flow as a throttle, this movement being under the direct control of the operator by means of a cable or similar linkage. The throttle slide is the chief metering component of the carburetor and determines the volume of fuel induced into the air passage.
On the CV unit, the throttle cable directly opens and closes a throttle plate, whereas the slide proper is caused to open and close in response to venturi vacuum. The moving slide adjusts the size of the venturi throat and therefore functions to proportion the ratio of fuel to air throughout most of the operating range. Attached to the slide is a tapered jet needle which is inserted in the fuel orifice to vary the amount of fuel allowed to pass into the engine, this action occurring primarily in the mid range.
Falling into the CV category is the Motor-Craft Ford VV 2700 carburetor, a double square slide-block venturi arrangement for two barrel applications. Both slide blocks have tapered needle fuel orifices and are controlled by a common vacuum motor.
In CV carburetor operation, the fuel-to-air ratio is varied as a function of the vacuum prevailing between the throttle and throat. Inasmuch as the "control" vacuum is not linearly proportional to air flow throughout the full operating range, for satisfactory performance it is necessary to include empirically-designed needle valve tapers and air jets as well as idle, slow speed, power and pump jets to establish and acceptable relationship between air and fuel throughout the full range.
In the throttle-plate carburetor, as the name implies, use is made of a pivoted plate in the throat of the main Venturi air passage, which plate combines the functions of air valve and throttle. The action is similar to the direct control type; hence to effect the necessary corrections, idle and low speed jets, mid-range and high speed jets as well as accelerating pump jets actuated by the throttle slide or pivote plate linkage are required.
Although all present types of slide-valve carburetors adjust their throat areas, the velocity-pressures attained at the low end are insufficient to draw fuel from the main jet ports or orifices, or needle-valve jets; hence auxiliary parts and jets are required for idle and slow speeds. Furthermore, they are designed to hold constant vacuum or constant velocity in the throat section, thereby relying on the position of the slide valve and its attached tapered needle valve position in the stationary orifice to control, fuel quantity above idle and slow speeds.
The serious deficiency common to all existing types of slide-valve carburetors is their inability to provide a fuel-to-air ratio appropriate to the varying conditions which prevail throughout the full range of engine operation. While auxiliary devices and other expedients have been used to overcome this deficiency, these not only render the carburetor structure relatively complex and more expensive to manufacture and to maintain, but they fall short of providing efficient and trouble-free carburetion throughout the full range.
In my copending application (A), there is disclosed a self-regulating automatic variable venturi carburetor for supplying a fuel-air mixture to the intake manifold of an internal combustion engine in a ratio appropriate to the prevailing conditions of engine speed and load throughout a wide operating range without the need for auxiliary devices and expedients. The structure includes a spring-biased axially-shiftable spool whose contoured inner surface has a venturi configuration to define a passage through which flows incoming air intermingled with fuel drawn or injected therein.
The axial position of the spool in relation to a stationary throat line in the main venturi passage determines the area of opening at the effective throat, this opening determining the magnitude of velocity-pressure. This spool is subjected to the hydrodynamic force produced by the air-fuel mixture flowing therethrough, this force acting against the spring to displace the spool to an extent producing an effective throat opening which results in a fuel-air ratio appropriate to the prevailing condition. The present invention also exploits the hydrodynamic force to operate an air valve in an automatic carburetor.